This invention relates in general to the field of synchronous switching operations in power lines. In particular, the present invention relates to a method and an apparatus for showing data representative of the accuracy of switching operations executed by a high-voltage switchgear operatively coupled to a synchronous switching device.
As it is well known, power systems for transmitting and distributing electricity from power sources to various loads and users are equipped with several types of protecting switchgear, such as high-voltage circuit breakers. Such switchgear is typically adapted for intervening under determined operating conditions so as to ensure a proper functioning of an associated power line and of loads/users connected therewith.
Voltage and current transients generated during switching of high-voltage circuit breakers are of increasing concern for the electric utility industry. These concerns include both power quality issues for voltage-sensitive customer loads, and excessive stresses on power system equipment. Some proposed solutions for reducing switching transients include circuit breaker pre-insertion devices, such as resistors or inductors, and fixed devices such as arresters and current limiting reactors.
A solution finding increasing popularity is the so-called synchronous switching method, sometimes also referred to as the point-on-wave switching. Synchronous switching is performed by dedicated electronic devices, indicated in the art as synchronous switching devices, which control the operations of the associated switchgear. Upon receiving a close or a trip command, a synchronous switching device delays the energization of the switchgear control coils by a few milliseconds. In this way, the current inception in the case of a close command, or the contact separation in the case of an opening or trip command, is expected to ideally coincide with a certain point on the AC wave which is known to reduce switching transients. In applications, operations are considered synchronous with the AC wave when the current inception or the separation of the contacts occurs within a narrow window around the desired point on the AC wave. For synchronous closing, this point is often the voltage zero crossing. Applications where it is beneficial to close the contacts on or near the voltage zero crossing include the energizing of capacitor banks and energizing of unloaded lines or cables. Synchronous opening can be employed for shunt reactors de-energizing as an example.
Synchronous switching devices are usually located in high-voltage or medium-voltage substations and are provided with a software which allows the communication with a user, for instance for receiving device specific data, displaying this data, composing device settings and sending these settings to the device. This software is usually referred to as user-interface software. In some cases, the software that allows the communication between the synchronous switching device and the user may be different from the software that presents the downloaded data.
For synchronous switching operations, on the user side, a corresponding user-interface software enables the user to receive records of synchronous operations, log entries, alarm status et cetera, from the synchronous switching device, and also displays this data in a user-friendly manner. The software also supports the user in selecting the synchronous switching device settings and can send the new settings to the device itself.
Clearly, users need to analyze the data in order to properly evaluate the performance of their equipment, and especially the accuracy of switching operations executed with respect to the desired synchronous or point-on wave switching operations. In other words, users wish to know how accurately the combination of a synchronous switching device and the associated switchgear was able to hit the targeted point-on-wave—not just for the most recent operation but also for as many operations as records are available.
Traditionally, user-interface software used with synchronous switching devices show data only in a numerical form. This makes it difficult for the user to grasp how accurately the synchronous switching device and the associated switchgear are performing on a statistical basis, and therefore to adopt appropriate corrective measures when needed.
Therefore, it would be desirable to provide a solution which allows the presentation to a user of a more accurate and complete picture regarding synchronous performance of a high-voltage switchgear, such as a high-voltage circuit breaker. This solution is provided by the method and apparatus according to the present invention.